Adiabatically changing conditions of an air stream are well known, the most common being operation of evaporative coolers wherein the temperature of an air stream is reduced by the evaporation of water. Evaporative coolers generally achieve less than ninety percent saturation of an air stream.
U.S. Pat. No. 5,718,848 offers improvements by employing multi-stages by passing air across a series of spaced parallel wetted wicks that repeatedly interrupt the air passage. As the temperature reduction is proportional to the increase in humidity of an air stream these devices can create excessive humidity in an air stream and this has led to indirectly cooling the primary air stream; a device often referred to as an indirect evaporative cooler. This also follows in the invention just mentioned wherein one air stream is cooled by heat transfer from a second air stream that is maintained nearly saturated with the air streams passing in cross flow.
A counter-flow device of the same basic operation is taught in U.S. Pat. No. 6,845,629 B1.
A cooler air delivery temperature is postulated in U.S. Pat. No. 7,093,452 B2 and U.S. Pat. No. 7,181,918 wherein a portion of the delivery air is returned to the wetted side of the indirect cooler.
A more sophisticated approach is taught in U.S. Pat. Nos. 4,977,753 and 7,197,887 where a portion of the supply air exits while being humidified in a cross flow and staged manner so as to approximate counter flow of the air streams. It is claimed that this configuration allows the final primary air stream to achieve conditions concurrent near the dew point temperature of the beginning air stream.
True counter flow of air streams wherein a portion of a primary air stream is saturated and returned parallel to the primary air stream is taught in a number of patents. For examples, U.S. Pat. No. 6,338,258 B1 incorporates fins to improve heat transfer while U.S. Pat. No. 6,845,629 B1 employs a common basin below the media where water is pumped to alternate chambers in a vertical arrangement. The patents behind these configurations also teach achieving near dew point temperatures of the beginning air stream.
Alternative structures are also presented. U.S. Pat. No. 7,228,891 B2 presents a ventilating system that includes a plurality of laminated plates formed in a mesh type to increase air turbulence in its cross flow configuration. U.S. Pat. No. 6,032,730 teaches forming a counter-flow heat exchanger paper members all having a moisture permeability including a plate-like partition interposed between aligned corrugated sheets.